Lung cancer is the leading cause of cancer mortality in the U.S. and woridwide with the majority of these cancers caused by smoking. The Multiethnic Cohort (MEC) study strongly demonstrated that there are major differences among US ethnic/racial groups in lung cancer risk associated with smoking. We will investigate the hypothesis that African Americans are more susceptible to the carcinogenic properties of tobacco-associated chemicals than European Americans as a result of reduced DNA repair capacity. This will be assessed by determining the sensitivity of lymphocytes from Africans or African Americans and European Americans to the toxic and mutagenic activity of activated forms ofthe three tobacco carcinogens, 4 (methylnitrosamino)-l-(S pyridyl)-1 butanone, benzo[a]pyrene and 1,S-butadiene. We will test our hypothesis by performing the following specific aims: 1. Determine if there is a difference in sensitivity between European Americans and Africans to the cytotoxic effects of activated tobacco smoke carcinogens using the International HapMap Epstein-Barr virus (EBV)-transformed B-lymphocyte cell lines derived from trios of European Americans (CEU) and Yoruban (African, YRI) populations; 2. Determine if there is a difference in sensitivity between European Americans and Africans to the genotoxic effects of activated tobacco smoke carcinogens using the HapMap B-lymphocyte cell lines; 3. Determine if there is a difference in repair rates for tobacco smoke-derived carcinogen DNA adducts between European Americans and Africans using the HapMap lymphocyte cell lines or lymphocytes isolated from European American and African American smokers in Project 5; 4. Perform candidate gene and genome-wide association studies of the toxicological phenotypes measured in Aims 1-3 to determine if specific genotypes drive the observed phenotypes in collaboration with Project 1. Collectively, these studies will reveal if there are ethnic/racial differences in repair of tobacco carcinogen derived DNA damage and if these differences in repair translate into differences in sensitivity to the genotoxic effects of these chemicals.